1. Field of the Invention
The present invention relates to a process for preparing a polyepoxide which can be cured in a short time by an epoxy resin hardener. The present polyepoxides are used for casting materials, varnishes, impregnants, bonding agents, sealing materials, powdered paints, fiber-resin composites, laminates, molding compounds, and the like with an epoxy resin hardener.
2. Description of the Prior Art
Because epoxy resins exhibit superior insulation properties, adhesiveness, high-temperature properties, corrosion inhibiting properties and mechanical strength, the resins are commonly used in many applications, for example, potting, encapsulating, coating, foaming, casting, caulking, molding, adhesives, tooling, and the like. In the manufacture of computors and small calculating instruments the electrical parts are sealed with an epoxide resin. For such applications the polyepoxide should be cured for a short time and give a cured product having superior high-temperature properties.
Several polyepoxides have been used in these applications, and they include a polyglycidylethernovolak resin ("Epicoat 154" available from Yuka Shell Epoxy Kabushiki Kaisha), a polyglycidylether-cresol-novolak resin ("EOCN" available from Nippon Kayaku Co., Ltd.), methylene-di-aniline-tetraepoxides, and polyepoxides of tri- or tetra-(hydroxyphenyl)alkanes. The cured products obtained from these polyepoxides have superior high-temperature properties, but these polyepoxides cure only over long periods of time.
It is also known that polyepoxides of tris(4-hydroxyphenyl)methane, the so called "Leucaurin Epoxides", can be cured with an epoxy resin hardener such as an aromatic amine, a polycarboxylic anhydride, or the like. The resulting product has a heat distortion temperature of more than 300.degree. C. (see U.S. Pat. No. 3,787,451). However, it takes sixteen hours to cure at 180.degree. C. A need therefore continues to exist for a polyepoxide material which rapidly cures while providing excellent physical and mechanical characteristics.